MioKontic: I'm sure I read somewhere that it's 10ft. And you are right, I think it's any club except the wedges - once you get to wedge distance you need to get closer to the hole to get a heartbeat.
I think if your distance to the hole is 100 yds or more, you'll get the heartbeat if your approach ends up within 10 feet of the hole. Inside of 100 yds, you'll get the heartbeat if your approach is within 5 feet of the hole.
That's just a general rule, though. I think for some shorter approaches (not sure what the cutoff is), you'll have to be even closer to the hole than that to get the heartbeat. And even then, the heartbeat is not always guaranteed. For example, earlier today I got the heartbeat on a greenside pitch from 11 yds that ended up 1.1 feet from the hole. But other times, I've pitched in from off the green and not gotten the heartbeat.
For putts, you'll get the heartbeat if your distance to the hole is 40 feet or more and your ball ends up within 1 foot of the hole.